Human serum albumin (HSA) is a non-glycosylated single chain protein consisting of 585 amino acids, having a molecular weight of 66.5 kD and an isoelectric point between 4.7-4.9. It is the most abundant protein in human blood plasma, making up about 60% of the total plasma proteins. There is about 40 g of HSA in per liter of human blood. Besides being present in the plasma, HSA is also found in tissues and body secretions, skins and lymph cavities. Under normal physiological conditions of human beings, HSA has an effect of maintaining plasma colloid osmotic pressure, nourishing, accelerating the concrescence of wounds, and as a carrier, participating in transportation of many hydrophobic biological molecules such as hormones, biological active substances and drugs in the blood. Therefore, HSA is an important medical protein that is mainly used clinically for the treatment of hypoproteinemia caused by loss of blood, burn, scald, plastic surgery and brain lesion, as well as for the treatment of liver cirrhosis, hydronephrosis and so on.
At present, HSA for clinical use is mainly prepared by extracting and isolating from human plasma. However, this preparation approach has the following disadvantages: on one hand, the source of plasma is insufficient, i.e. the limited blood supply is unable to meet the demands of production of HSA and the relevant preparations thereof; on the other hand, blood itself may potentially be a risk factor, for example, it may contain dangerous infectious pathogens such as hepatitis virus, human immunodeficiency virus (HIV) and so on, which causes enormously concerns about the application of HSA extracted from plasma.
With the development of modern DNA recombinant and synthesis techniques, the researchers take a profound interest in the production and application of recombinant human serum albumin (OsrHSA). So far, people have tried to use various expression systems for mass production of OsrHSA. For example, prokaryotes such as E. coli (Latta, M. et al., Bio/Technology, 5:1309-1314, (1987)), Bacillus subtilis (Saunders, C. W. et al, J. Bacteriol. 169: 2917-2925, (1987)), eukaryotes such as yeasts (WO 00/44772, EP0683233A2, U.S. Pat. No. 5,612,196) and cultivation of animal cells have been used for the production of OsrHSA. However, such approaches are not suitable for industrial production due to low expression level or high production cost.
Chinese patent application No. 201010606635.8 of the present inventors discloses a method for extracting OsrHSA from rice. Based on the method, the present invention further studies the process for removing endotoxin from OsrHSA and improving the protein purity >99.9999%, thereby obtaining this novel technical solution of the present invention. The application No. 201010606635.8 is specifically incorporated herein and is to be used for all purposes consistent with incorporation by reference.